Printer

Abstract

 In an apparatus 1 and a method for applying a medium to a substrate 41, in an origination station 3, an application pattern is generated electronically. A mimeograph stencil 7 is cut in the form of the application pattern by thermal print means 13. The cut stencil is transferred to an application station. There, the medium is applied to the substrate through the cut stencil.

Description

[0001] The present invention relates to an apparatus and method for applying a medium to a substrate, for example glue or ink to a carton or packing case.

[0002] Cartons and cases are frequently printed with inks of one or more colours to convey the origin or identity of their contents and sometimes also to give them an attractive appearance. Often, they are assembled and then closed by application of glue. It is convenient to apply the glue by means of a "printing" process in the same way as ink is applied.

[0003] High quality printing is often used to decorate labels to be applied to packaging, for example utilising offset lithography or rotogravure printing on a suitable medium. Packing cases or outers are usually made from corrugated board which comprises a very high percentage of recycled pulp for cheapness. The corrugation nevertheless provides a high degree of strength. Such cases are often printed by the flexographic method which is relatively cheap. Although it cannot achieve the very high resolution of offset lithography or rotogravure, it is more than adequate for the kind of decoration normally required for cases. Another technique sometimes used for cases is ink-jet printing.

[0004] Cartons and cases are normally printed by a converter (packaging supplier) who prints and cuts the appropriate blanks on the relevant substrate which may be in individual sheet form or fed from a roll, depending on the particular substrate material. The printed and cut blanks are usually then delivered flat to the customer who assemblies and fills them. Ink jet printing is sometimes done by the customer.

[0005] Glue is normally applied in the customer's factory, unless the cartons or cases are delivered part-assembled, in which the initial glueing is done by the converter and the final glueing for closing the carton or case is subsequently done during or after filling at the customer location.

[0006] Ink jet printing, although fairly flexible, is restricted in its print area and resolution. It also requires a high level of maintenance. Flexographic printing requires a large initial capital investment and needs to be operated by specially trained personnel. Quick changeovers of artwork are not possible and the masters have to be prepared on complicated equipment.

[0007] Although lithography or gravure printing of labels produces superior print quality, the capital outlay required and running costs are even higher than for ink-jet printing or flexography. They also necessitate the operators having a high level of technical expertise. Flexibility of changeovers is also compromised because it is necessary for the packer always to maintain an adequate stock of all possible label types which might be needed. These drawbacks make such techniques unsuitable for low cost packaging.

[0008] Thus, there is a need to produce high quality printing direct onto substrates such as packaging, during the manufacturing, packing and distribution process.

[0009] Traditional methods of applying glue, such as rollers, jets, pads and the like, require changing or resetting to other glue patterns. They provide relatively poor control of the amount of glue applied and require frequent and regular cleaning of the rollers, jets or pads etc.

[0010] The present invention is suited to applying any desired medium, whether ink, glue or any other substance, for example in liquid, semi-liquid or paste form, to a substrate. The substrate may be board, paper or any other appropriate material.

[0011] In its various aspects to be defined and described hereinbelow, the present invention employs stencil mimeography and overcomes the drawbacks of the known printing and glueing techniques referred to above.

[0012] Stencil mimeography is a technique which has previously been restricted to photocopying and duplicating machines. It involves burning a pattern in a suitable stencil material using a thermal print bar. The bar comprises discrete cells which can be energised selectively to form the desired pattern on the stencil material.

[0013] Thus, in a first aspect, the present invention provides a method of applying a medium to a substrate, the method comprising in an origination station, electronically generating an application pattern and cutting a mimeograph stencil in the form of the application pattern by using thermal print means, transferring the cut stencil to an application station and there, applying the medium to the substrate through the cut stencil.

[0014] In general, the present invention both comprises methods of applying a medium to a substrate and apparatus for carrying out these methods.

[0015] Thus, the first aspect of the present invention also provides apparatus for applying a medium to a substrate, the apparatus comprising an origination station comprising electronic means for generating an application pattern and thermal print means responsive to the electronic means, for cutting a mimeograph stencil in the form of the application pattern, the apparatus further comprising means for transferring the stencil to an application station comprising means for applying the medium to the substrate through the cut stencil.

[0016] Preferably, the application pattern is stored in a computer memory. The computer may be used to generate the pattern or the pattern may be externally generated and transferred to the memory. The thermal print means is then energised by an interface circuit in response to the contents of the memory.

[0017] Another useful feature is obtained by providing the print drum with an internal screw conveyor. Indeed, a second aspect of the present invention provides a print drum having a porous surface and an internal screw conveyor for conveying a medium to the inside of the porous surface to be exuded therethrough. The second aspect of the present invention also includes a method of applying a medium to a substrate, using such a print drum.

[0018] An especially preferred configuration of such a screw conveyor comprises an Archimedes screw arrangement. One of the screw and drum will be driven and the other fixed. The choice of arrangement will depend inter alia on the application and the size of drum required.

[0019] Superior flow and application properties can be obtained if the porous surface comprises a plurality of overlapping progressively finer screens, with the coarsest on the inside surface. Most preferably, at least one of these screens is made of a resilient material.

[0020] An especially preferred application of either aspect of the present invention comprises applying the medium, eg ink or glue, direct onto packaging on a packing line. For this and other applications, it is especially advantageous to utilise a print drum with its axis of symmetry arranged substantially vertically. The drum may be built into a material handling system of the packing line.

[0021] In the origination station, the stencil may be cut automatically to a desired length and automatically wrapped around the drum in the application station. Preferably also, after use, the stencil is automatically removed from the drum and automatically compressed into a container.

[0022] The present invention will now be illustrated in more detail by the following description of a preferred embodiment and with reference to the accompanying drawing, in which:-

Figure 1 shows an apparatus according to the present invention and for performing a method according to the present invention;

Figure 2 shows a mechanism for discarding a used stencil from the apparatus shown in Figure 1;

Figure 3 shows a preferred form of print drum construction for use in the apparatus shown in Figure 1;

Figure 4 shows the surface construction of the drum shown in Figure 3; and

Figure 5 shows the apparatus shown in Figures 1-4, mounted on a conveyor.

[0023] Figure 1 shows an apparatus 1 comprising an origination station 3 and an application station 5.

[0024] The origination station 3 comprises a reel 7 of stencil material 9 and a cutting device 11. The cutting device comprises a thermal print bar 13 connected to an interface circuit 15 which is connected via a link 17 to a computer 19.

[0025] At the application station, a rotatable drum 21 is provided with a porous surface 23. The drum is situated adjacent a pressure roller. The drum and the roller are arranged to be driven by a belt 25 connected to a motor 27. The motor is arranged to operate under the control of an electronic circuit 29.

[0026] The motor is also connected to drive a transport mechanism 31 comprising a further belt 33 and further pairs of rollers 35, 37, A container 39 is situated adjacent the drum, remote from the origination station.

[0027] In use, the stencil material 9 is fed from the reel 17 to the cutting device 11. In an alternative embodiment, the stencil material may be fed from a stock of same. The thermal print bar 13 of the cutting device contains an array of discrete elements or pixels (not shown) which are selectively energised by the interface circuit 15 under the control of the computer.

[0028] The stencil material comprises two or more layers. The outer layer is impervious to the application medium such as ink or glue, yet will melt, evaporate or dissolve when subjected to the heat from the thermal print bar. The outer layer of the stencil material is bonded to a layer of porous material which absorbs the medium from the porous drum surface 23. The outer layer may for example comprise a wax, polyester or polyvinylchloride thermoplastics resin. The porous layer may for example comprise polyester or polyamide fibres.

[0029] A pattern, such as a glueing or printing pattern may be stored in the memory of the computer 19. A programme in the computer allows the stored pattern to be modified as desired, eg. in terms of scale (overall size) or in any other way. The pattern may be loaded into the computer memory after being generated at an external source or an appropriate programme may be provided to enable the user to create the pattern within the computer.

[0030] The computer controls the selective energisation of the print bar pixels via the interface circuit. The heating of the pixels causes the desired pattern to be cut (burned) into the stencil material.

[0031] After the pattern has been cut into the stencil, the latter is cut to suitable length by cutting means (not shown) and is wrapped around the drum 4. A sheet substrate material such as packing case blanks 41 is fed between the drum and the pressure roller, conveyed by the rollers 35, 37 of the transport system. Under the control of the electronic circuit 29, print pressure roller 42 brings the substrate 41 into contact with the drum. Simultaneously, medium such as ink or glue is applied through the centre of the drum, through the porous surface thereof to be selectively applied to the surface of the substrate in the desired pattern, through the stencil.

[0032] When a print run is complete, or when the stencil becomes worn after extensive use, it is automatically removed and compressed into the container 39. This is effected as shown in Figure 2.

[0033] Normally, the stencil is retained on the drum by a clamping mechanism 44. When it is desired to remove the stencil, the mechanism is released so that the free end 43 of the stencil drifts away from the drum. Then, a solenoid 45 causes a movable roller 49 to pinch the stencil between itself and a fixed roller 51. At least one of the rollers is driven to force the discarded stencil into the container 39.

[0034] Referring now to Figure 3, this shows a preferred construction of the print drum for use in a substantially vertical orientation, that is, with its axis of symmetry substantially upright.

[0035] The drum 21 with porous surface 23 is substantially hollow and encloses an Archimedes-type screw 53 mounted on a rotatable shaft 55 which is driven by a motor 57 and terminates in an end flange 59. As stated hereinbefore, in the alternative, the drum may be rotatably driven, relative to the screw. This arrangement transfers the application medium from a reservoir 59 to be spread around the inside of the porous drum surface 23.

[0036] The amount of medium applied in a unit time to the inside of the drum will be determined by the separation X between the screw and the inside of the drum. To accommodate a wide range of viscosities of the medium, the pitch Y of the screw may be varied.

[0037] Figure 4 shows the construction of the porous drum surface 23. It comprises a perforated cylinder 61 around which is wrapped a coarse mesh screen 63. Progressively finer screens 65, 67 are then wrapped over one another until the desired flow characteristics for the particular stencil material are achieved.

[0038] At least one of the screen layers is formed with resilient properties to facilitate printing on coarse surfaces, or on surfaces with undulations. Thus, the apparatus can cope with a wide variety of substrates.

[0039] Figure 5 shows how an upright configuration of print drum enables in-line direct printing on packages.

[0040] The drum 21 may be freely supported but is preferably attached to a conveyor 69 of a material handling system. As a pack 71 passes the drum, the latter is put into contact with the latter by means 73, for example operated under spring pressure, pneumatic pressure or the like. The roller may rotate freely by virtue of its contact with the moving pack, or may be rotatably driven. Alternatively, the pack may be held stationary whilst the print drum is driven over it.

[0041] Changing the system configuration allows it to handle any desired substrate, for example bottles, cans, boxes, trays, rolls of plastics film, paper or foil etc

Claims

1. A method of applying a medium to a substrate, the method comprising
   in an origination station, electronically generating an application pattern and cutting a mimeograph stencil in the form of the application pattern by using thermal print means, and
   transferring the cut stencil to an application and there, applying the medium to the substrate through the cut stencil.

2. A method according to claim 1 wherein the application pattern is stored in a computer memory and the thermal print means is energised by an interface circuit in response to the memory contents.

3. A method according to either preceding claim, wherein in the origination station, the stencil is cut to a required length and is subsequently automatically wrapped around a drum in the application station.

4. A method according to claim 3, wherein after use, the stencil is automatically removed from the drum and automatically compressed into a container.

5. An apparatus for applying a medium to a substrate, the apparatus comprising:
   an origination comprising electronic means for generating an application pattern and thermal print means responsive to the electronic means, for cutting a mimeography stencil in the form of the application pattern;
   means for transferring the stencil to an application station; and
   the application station comprising means for applying the medium to the substrate through the cut stencil.

6. An apparatus according to claim 5, further comprising a computer memory for storing the application pattern and an interface circuit for energising the thermal print means in response to the memory contents.

7. An apparatus according to claim 5 or claim 6, wherein the origination station comprises means for cutting the stencil to a desired length and the application station comprises a drum and means for automatically wrapping the cut stencil around the drum.

8. An apparatus according to claim 7, wherein the application station comprises means for automatically removing the stencil from the drum after use and means for automatically compressing the removed stencil into a container.

9. An apparatus according to any of claims 5-7, wherein the origination station comprises a print drum having a porous surface and an internal screw conveyor for conveying the medium to the inside of the porous surface to be exuded therethrough.

10. A print drum having a porous surface and an internal screw conveyor for conveying a medium to the inside of the porous surface to be exuded therethrough.

11. An apparatus according to claim 9 or a print drum according to claim 10, wherein the print drum is arranged with its axis of symmetry substantially vertical.

Drawing